lpd(ADMN)

lpd -- line printer daemon

Syntax

/usr/lib/lpd [ -ld ] [ port # ]

Description

lpd is the line printer daemon (spool area handler) and is normally invoked at boot time from the /etc/rc2.d/S85tcp file which is an rc2(ADM) startup script. It makes a single pass through the printcap(SFF) file to find out the existing printers and prints any files left after a crash. It then uses the system calls listen(SSC) and accept(SSC) to receive requests to print files in the queue, transfer files to the spooling area, display the queue, or remove jobs from the queue. In each case, lpd forks a child to handle the request so the parent can continue to listen for more requests. The -l flag causes lpd to log valid requests received from the network. This can be useful for debugging purposes. The -d option turns on socket-level debugging.

Access control is provided by two means. First, all requests must come from one of the machines listed in the file /etc/hosts.equiv or /etc/hosts.lpd. Second, if the ``rs'' capability is specified in the printcap entry for the printer being accessed, lp requests will only be honored for those users with accounts on the machine with the printer.

NOTE: There are other configurable options that apply to the /etc/printcap file. Refer to the printcap(SFF) reference manual page for more information.

If the file minfree exists in a printer's spool directory on the destination machine, it should contain the number of minimum disk blocks that must be free in addition to the actual size of the print job. If the sum of this number of minimum disk blocks and the job size exceed the available free space of the device on which the spool directory exists, then the job will not be processed. Superuser privileges are required to create and edit the minfree file in the spool directories.

The file lock in each spool directory prevents multiple daemons from becoming active simultaneously, and stores information about the daemon process for lp(C), lpstat(C), and cancel(C). After the daemon has successfully set the lock, it scans the directory for files beginning with cf. Lines in each cf file specify files to be printed or non-printing actions to be performed. Each such line begins with a key character to specify what to do with the remainder of the line.

C: Classification. String to be used for the classification line on the burst page.
F: Content type support.
H: Hostname of the machine where lp was invoked.
I: Indent output by amount.
J: Job name. String to be used for the job name on the burst page.
L: Literal. The line contains identification info from the password file and causes the banner page to be printed.
M: Mail specified user when the current print job completes.
N: Name of file used by lpq (Pass 2 only).
O: Other System V options; for example ``nobanner''.
P: Person. Login name of the person who invoked lp. This is used to verify ownership by cancel.
Q: Queue. Priority level in print queue.
S: Stat info. For symbolic link protection.
T: Title. String to be used as the title for pr(C).
U: Unlink. Name of file to remove upon completion of printing.
W: Width. Page width.
c: Cifplot file to print.
d: dvi file to print.
f: Formatted file. Name of a file to print which is already formatted.
g: plot file to print.
l: Filename of text file with control characters.
n: ditroff file to print
p: Filename of text file to print with pr(C).
r: Request ID used by the cancel(C) command.
t: troff file to print.
v: Plain raster file to print.
1: Roman font file for troff.
2: Italic font file for troff.
3: Bold font file for troff.
4: Sanserif font file for troff.

If a file can not be opened, a message will be logged in the file /usr/adm/syslog via syslog(SLIB) using the LOG_LPR facility. lpd will try up to 20 times to reopen a file it expects to be there, after which it will skip the file to be printed.

lpd uses fcntl(S) to provide exclusive access to the lock file and to prevent multiple daemons from becoming active simultaneously. If the daemon should be killed or die unexpectedly, the lock file need not be removed. The lock file is kept in a readable ASCII form and contains two lines. The first is the process ID of the daemon and the second is the control filename of the current job being printed. The second line is updated to reflect the current status of lpd for the programs lpstat(C) and cancel(C).

Files

/etc/printcap: printer description file
/usr/spool/: spool directories
/usr/spool/lpd/<printer_name//minfree: minimum free space to leave
/dev/lp: line printer devices
/etc/hosts.equiv: machine names allowed printer access
/etc/hosts.lpd: machine names allowed printer access, but not under same administrative control

Standards conformance

lpd is conformant with:

RFC 1179
X/Open Portability Guide, Issue 4, 1992

lpd(ADMN)

Syntax

Description

Files

See also

Standards conformance